Multimethod Microstructural Diagnostics of Polymer Electrolyte Membrane Water Electrolysis Cell Components Uncovering Diverging Degradation Pathways After Short‐Term Testing

Performance degradation of polymer electrolyte membrane water electrolysis under different operating conditions has attracted increased interest in the field of green hydrogen. While the main degradation mechanisms, for example, anode catalyst dissolution and membrane radical degradation, have been widely discussed, a comprehensive analysis of all possible degradation mechanisms is still necessary to differentiate electrochemical data. In this article, we present an in‐depth, multimethod investigation into two samples with similar electrochemical behavior after ~3.5 days at different current profiles. A combination of electrical measurements, electron microscopy, and spectroscopy is employed. Although Ti porous transport layer passivation emerges as the primary degradation mechanism for both profiles, secondary mechanisms such as Pt catalyst passivation, membrane degradation by contaminants and radical attack, and anode catalyst dissolution differ between the two profiles. While they do not contribute to electrochemical performance degradation after short‐term testing, they indicate possible problem areas for long‐term testing. All further degradation mechanisms concerning the membrane electrode assembly can be discarded based on the results. This study highlights the necessity of degradation diagnostics, especially during short testing times, because the electrochemical data alone was not sufficient to show differences between the profiles, and secondary degradation mechanisms that will cause problems in long‐term operation were flagged.